The model of fluid membrane shall be examined in detail with the disk membranes of bovine rod outer segment (ROS). Three dynamic parameters of the system will be measured by quasielastic light scattering method. They are 1) membrane surface undulation, 2) intralamellar translational diffusion and 3) rotatory diffusion of rhodopsin. The first will characterize the degree of flexibility of the surface structure and the second will quantify the intralamellar fluidity. The rotatory diffusion will serve to relate local dynamics of the membrane to the photoreceptor function either coupled through or independent of the other two variables. Relevant changes of these parameters in the unbleached and bleached states will be elucidated in order to determine their relative significance for the visual cycle. The technique is capable of probing the dynamic structure of membranes with negligible perturbation as long as the thermal equilibrium is established and the motions accompany changes in polarizabilities. Furthermore, the extraction of quantitative information requires no assumptions about the binding of photopigment chromophore to the protein component, rhodopsin, and about the structural rigidity of lamellar surface. It requires however the planar alignment of disk membranes relative to the appropriate pair of polarization directions of the incident and scattered light.